The present invention relates generally to cameras, and more particularly to an improved ranging system for sighting variably positioned objects through a camera viewfinder.
Prior to the development of mechanical ranging means, it was known to measure camera range intrinsically by reliance upon variable external markings. Portrait photographers, for instance, measured the distance between a subject's chin and forehead to determine the appropriate camera range. This method, of course is tedious and only particularly suited to fixed object photography.
Therefore, mechanical ranging means such as "variable sighting circles" have been developed to provide the photographer with an adjustable reference value for picture taking. The principle of operation of this type mechanical means includes a lens and mirror combination which reflects a marking, such as a circular mask or the like, into the camera viewfinder. In practice, the corresponding mirror image sighting circle projected into the camera viewfinder diametrically adjusts to the orientation of the reflected mark. To assure a sharp reflection of the mark in the viewfinder, an aspherical lens is mounted between the mark and reflecting mirror and projects a sharp image of the mark in all positions thereof.
In connection with this type device, the camera is focused by adjusting the marking member until, for instance, the sighting circle surrounds, for example, the head of the subject to be photographed. This focusing method is based upon the fact that adults and children have substantially the same head size, and the size differences thereof have no significant effect upon the sharpness of focus of the camera.
The principal disadvantage of this type device is the requirement of the aspherical lens mounted between the mask and mirror for sharp image formation in the camera viewfinder. The need for the aspherical lens severely escalates the cost of the system.
Other types of devices whose principles of operation rely upon adjusting to objects of previously known size are similarly very expensive.
Accordingly, the instant invention provides a ranging system of the type generally heretofore described which overcomes the disadvantages of the prior devices, which is uniquely but simply constructed and economically practical.